Coal feedstocks

The main difference between gas works and coke oven practice is that, in a gas works, maximum gas yield is a primary consideration whereas in the coke works the quality of the coke is the first consideration. These effects are obtained by choice of a coal feedstock that is suitable to the task. For example, use of lower volatile coals in coke ovens, compared to coals used in gas works, produces lower yields of gas when operating at the same temperatures. In addition, the choice of heating (carbonizing) conditions and the type of retort also play a principal role (10,35). 

Process Pa.ra.meters, The most notable effects ia gasifiers are those of pressure (Fig. 1) and coal character. Some initial processiag of the coal feedstock maybe requited. The type and degree of pretreatment is a function of the process and/or the type of coal (see Coal conversion processes, CLEANING AND DESULFURIZATION). 

There is an inherent economic penalty associated with producing Hquids from either natural gas or soHd coal feedstock. Synthetic Hquid fuels technologies are generally not economically competitive with cmde oil processing in the absence of extraneous influences such as price supports or regulations. 

The hquid remaining after the solvent has been recovered is a heavy residual fuel called solvent-refined coal, containing less than 0.8 wt % sulfur and 0.1 wt % ash. It melts at ca 177°C and has a heating value of ca 37 MJ/kg (16,000 Btu/lb), regardless of the quaUty of the coal feedstock. The activity of the solvent is apparently more important than the action of gaseous hydrogen ia this type of uncatalyzed hydrogenation. Research has been directed to the use of petroleum-derived aromatic oils as start-up solvents (118). 

Pyrolysis processes can be divided into two groups low temperature and high temperature. The products of pyrolysis processes differ and can be controlled by temperature and the rate of material heating. Table 4.1 provides a summary of variations of the product slate for biomass and coal feedstocks. 

Practical conversion processes can only approach the theoretical efficiencies shown in Table 3. The coal conversion reactions do not proceed to completion at ambient temperatures within practical time limitations. As a result, a portion of the coal feedstock must be burned to supply heat so that the reactions can be carried out at elevated temperatures and pressure where the rates of conversion are rapid. In practical systems, this additional heat can only be partially recovered. Consequently, practical conversion processes have actual heat recovery efficiencies of about 60-70% for production of high H/C ratio products. Production of secondary fuels having somewhat lower H/C ratio, i.e. about 2.0, permits attainment of heat recovery efficiencies of 70 to 80j. 

This study shows that limited oxidation at 373 K or weathering (ambient) of coal feedstock reduces the thermoplastic properties of a coal This is manifest as a transformation in char type, from cenospheres to inertoids, at high rates of heating (10 -10 K s" ) in an Entrained Flow Reactor at 1273 K. The specific types of char are related to the chemical structure of the coal and an inverse relationship exists between the occurrence of cenospheric chars and the atomic 0/C ratio of the oxidised or weathered coal from which they are derived... 

The overall objective of this study is to investigate the effect of oxidation at 373 K, using static air, and weathering, under atmospheric conditions, upon the pyrolysis and combustion of pulverised coal feedstock using laboratory-based equipment. More specifically ... 

The plant processes 26,840 TPSD of low sulfur North Dakota lignite. The sulfur is 1.3 wt%/DAF coal. The coal analysis is shown in Table II. Output from the plant is 268,700 MM Btu/day of SNG, equivalent to 45,000 BOE/day. Total production of by-product elemental sulfur is 161 tons/day. This represents 78 wt% of total sulfur input from the coal feedstock. Since goal gasification and indirect liquefaction facilities are most likely to use Western low sulfur lignite or subbituminous coals, this represents the low sulfur case for coal conversion. 

In recent years several commercial plants have been constructed for conversion of coal to synthesis gas for chemical manufacturing. These include the Eastman Chemical s acetic anhydride plant, the Ube (Japan) ammonia plant, the SAR (Germany) oxo chemicals plant, and several coal to ammonia plants in China (e.g., Weihe, Huainan, and Lunan). The Ube plant and the SAR plant have since converted to lower-cost opportunity fuels (petroleum coke and residues). The Eastman plant is still operating exclusively on coal. Feedstock changes at the other plants illustrate the vulnerability of coal conversion processes to a changing economic climate. The fact that the Eastman process remains competitive under changing conditions is due to a set of special circumstances that favor a coal-based process. The success of the Eastman chemicals from coal complex demonstrates that synthesis gas from coal is a viable feedstock for some industrial chemicals under certain conditions. 

In 2000 Farmland Industries in Kansas started up a petroleum coke gasification plant to make ammonia. The plant uses Texaco s process to make 1000 tonnes per day of ammonia.185, 186 In 2004 Rentech purchased an 830-tonne-per-day ammonia plant in Illinois and plans to convert it from natural gas to coal feedstock. Startup of the conversion is expected in 20 07.300... 

During the conversion of coal to coke required for the production of pig iron, crude gases or coke oven gases are formed, together with benzols and tars (coal tars). The carbonization balance depends on the volatile matter index of the coal feedstock. On the average, one ton of dry coal yields ... 

Liuzhou Chemical Industry Corporation, Siuzhou, Guangxi, PRC — This gasifier uses a Shell design based on coal feedstock and converts 1,200 t/d of coal into 2.1 x 10 NmVd of syngas. The syngas is used to manufacture ammonia-based fertilizer and oxo-alcohols. Some process CO2 is recovered and used to make urea fertilizer. 

Sinopec, Zhijiang, Hubei, and Anqing, Anhui, PRC — These gasification facilities are scheduled to be built based on Shell gasifiers and will use coal feedstock to manufacture fertilizer. 

Since in some processes with coal feedstock (e.g., the Lurgi Process) the reaction according to Equation (61) may proceed to a considerable extent, they are more often referred to as coal gasification rather than as partial oxidation, but this is just a matter of definition. 

Oil Shale and Solvent-Refined Coal Feedstocks and Solid Effluents. 

The fuel product of this process has a very consistent heating value of 16,000 Btu per pound regardless of the coal feedstock to the process. This uniformity has been demonstrated in pilot productions from both... 

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